1. Field of the Invention
The present invention relates to a knee-protecting airbag which is folded and housed in front of knees of a seated occupant, and deploys with inflation gas for protecting the knees in the event of collision of the vehicle.
2. Description of the Related Art
A knee-protecting airbag in the prior art includes a bag-shaped airbag body inflatable with inflation gas and a tether located within the airbag body, as disclosed in JP 2002-337649 A.
The airbag body of this airbag includes a first wall located toward the occupant and a second wall located toward a vehicle body, each upon deployment. The lower part of the airbag body serves as an upstream of flowing-in inflation gas, and the upper part serves as a downstream of inflation gas. The tether joins the occupant's side wall and the vehicle body side wall together for keeping the airbag body substantially flat when inflated.
The tether is band shaped, and arranged along the transverse direction within the airbag body while leaving spaces between its left and right ends and the left and right edges of the airbag in the circumference of the airbag body as passages for inflation gas to flow upward therethrough such that the airbag body is developed widely in the transverse direction in the initial stage of inflation.
Moreover, the tether is provided in the vicinity of its transverse center with a gas communication hole such that inflation gas can flow upward therethrough and the airbag body secures certain extent of cushioning property in a portion right above the tether in the initial stage of inflation.
However, for structural reasons of vehicle, the knee-protecting airbag device sometimes cannot be located right in front of a seated occupant. In that event, the transverse center of the knee-protecting airbag is not placed to face the center of the occupant when deployed.
Moreover, although the knee-protecting airbag is adapted to protect occupant's knees advancing forward, the knees have sometimes been already positioned forward by the time the airbag device is actuated. In that event, the airbag has to be thrust in between a vehicle structural member and the knees smoothly while exerting cushioning property.
Yet another knee-protecting airbag in the prior art disclosed in WO 02/04261 is formed by sewing up the outer edges of an occupant's side base cloth and a vehicle body side base cloth having similar shapes to each other and made of woven fabric. When deployed, the upper edge of this airbag extends substantially straightly along the transverse direction.
Furthermore, an airbag disclosed in JP 52-5126 A which exemplifies a type of airbag formed by sewing up the outer edges of two base cloths of woven fabric has yarn directions of the base cloth dislocated by 45° from each other when overlaying one base cloth on the other, such that the airbag maintains a disc-shape without being twisted or slanted when inflated.
However, the knee-protecting airbag in the prior art has a substantially rectangular plate shape upon deployment, and the lower end of the airbag is fixed to the vehicle body while the upper end is left as a free end. Accordingly, the airbag has to be mounted on the vehicle considering interferences with surrounding members so as not to complete inflation with its upper end twisted or slanted.
Moreover, although the airbag formed by sewing up the outer edges of two base cloths is able to complete inflation without twisting or slanting, this type of airbag is mainly for steering wheel, and is formed by sewing up round base cloths. Accordingly, the arrangement of dislocating yarn directions of base cloths at 45° from each other is hard to apply immediately to a knee-protecting airbag to be inflated in a substantially rectangular plate shape and having a free end.